The present invention relates to apparatus for measuring the temperature of an object or specimen viewed through a microscope, and more particularly to the measurment of transformation temperatures of the object or specimen. Such measurements find applications in, namely, mineralogy, petrochemistry, microchemistry, biology and biochemistry, in a temperature range of -180.degree. to +600.degree. C.
In order to carry out such measurements, there is generally used a thermally controlled stage or object support comprising a thick platen provided with heating and cooling means, a specimen chamber in thermal contact with the platen, the specimen chamber being provided with thermometric means. The specimen is placed in the specimen chamber which has a transparent viewing window for microscopic observations. The specimen is thus brought to the temperature prevailing in the specimen chamber, this temperature being measured by the thermometric means and regulated by adjusting the heating power furnished by the heating means for temperatures above ambient temperature or the cooling power by cooling means for temperatures below ambient temperature. The thermometric means obviously must be able to measure very accurately the temperature in the relevant operating range, and the thermosensitive element associated with the thermometric device must not markedly affect the temperature taken in the specimen chamber.
Mercury thermometers having suitable accuracy in their working range are frequently used.
For diascopic lighting of the specimen, the platen is provided with a lighting well superposing a transparent specimen supporting plate in the specimen chamber. The condenser of the microscope penetrates into the lighting well so as to concentrate the illuminating beam on the specimen being observed.
For displacing the specimen in the viewing field of the microscope, the specimen chamber is generally provided with a mchanism for imparting translatory motion on the transparent specimen supporting plate, this mechanism comprising micrometric screws acting in two mutually perpendicular directions on the mounting of the transparent specimen supporting plate.
The heating means for the platen is usually a resistance heater embedded in the platen and supplied by an adjustable power supply means through an adjustable autotransformer. The cooling means is very often a passageway in the platen for carrying a coolant, for example, water or carbon dioxide expanded from its pressurized liquid state.
According to other known setups, the thermally controlled specimen holder or stage does not enable accurate temperature measurements in a wide range. At temperatures substantially remote from ambient temperature, the flow of energy between the platen and the chamber gives rise to temperature gradients which introduce errors in the measurements, particularly when the temperature changes rapidly, because the differences between the temperatures read and the temperature of the specimen are a function of the direction and the rate of change and, therefore, cannot be compensated for by a simple conversion. At high temperatures the heating of the optical and mechanical parts of the setup creates difficulties; the frosting of the optical elements by condensation of water vapor from the surroundings and the freezing of the cooling pipes interfere with low temperature operation. In fact, with known thermally controlled specimen holders for thermometric microscopic observations, the working temperature range is between -20.degree.C and +350.degree.C, but the accuracy of readings at the extreme limits of this range is poor.